The invention relates to a multicomponent glass for light-transmitting bodies, for use as core glass in glass fibers.
Optical components using light transmission fibers as a light path are usable in variable fields. Due to the special requirements imposed on their application, only certain cadmium-containing multicomponent glasses are currently available commercially for use as core glasses in glass fibers for twisters and tapers. For example, a large difference of refractive index between core glass and cladding glass is desirable. The larger this difference, the thinner the twister or the taper can be. Furthermore, this application imposes specific requirements on, inter alia, expansion, hardness and crystallization. Glass fibers made of multicomponent glasses tending to crystallize have, for example, considerable scattering losses.
As cadmium is more and more prohibited, there is a need for cadmium-free core glasses having further comparable or better properties.
It is therefore an object of the invention to provide cadmium-free multicomponent glass composition ranges within which glass compositions can be found which are particularly suitable as core glass in twisters and tapers.
This object of the invention is realized when a multicomponent glass is characterized by the composition as defined in claim 1.
Within the indicated range of composition, particularly glasses can be produced with a refractive index n of at least 1.75 and an (American) softening point of between 525xc2x0 C. and 725xc2x0 C. and particularly between 600xc2x0 C. and 725xc2x0 C.
The invention also relates to a glass fiber for light transmission, a twister or a taper, characterized in that the core components consist of a glass having a composition as defined according to the invention. The invention also relates to night-vision binoculars with such a twister.
A characteristic feature of the composition of the (core) glass according to the invention is that it comprises B2O3, ZnO, La2O3 and/or As2O3, La2O3 or another rare earth (lanthanide) oxide, and ZrO2 and/or HfO2 as main constituents, and Sb2O3 and/or As2O3. La2O3 or another rare earth oxide (including Y2O3) functions as a glass shaper in this case.
The glass according to the invention preferably comprises no or a minimal quantity of oxides of Na, K, Li and Cs because they soften the glass and decrease the refractive index.
In accordance with a first embodiment, the glass complies with the composition as defined in claim 5.
In accordance with a second embodiment, the glass complies with the composition as defined in claim 6.
In accordance with a third embodiment, the glass complies with the composition as defined in claim 7.
A characteristic feature of the first embodiment is the slightly higher refractive index n which may range between 1.75 and 1.79, in combination with favorable values of the coefficient of expansion xcex1 (30xc2x0 C. to 300xc2x0 C.) which may be in the range of 67 to 73xc3x9710xe2x88x927 Kxe2x88x921, and the viscosity (American softening point ranging between 675xc2x0 C. and 725xc2x0 C.).
A characteristic feature of the second embodiment is the even slightly higher refractive index (1.76 to 1.79) in combination with a value of xcex1 in the range of 63 to 71xc3x9710xe2x88x927 Kxe2x88x921, and an American softening point of between 600xc2x0 C. and 690xc2x0 C.
A characteristic feature of the third embodiment are the even higher values of the refractive index that can be achieved, in combination with a value of xcex1 in the range of 65 to 73xc3x9710xe2x88x927 Kxe2x88x921, and an American softening point of between 650xc2x0 C. and 725xc2x0 C.
The main constituents in said compositions are necessary to give the Cd-free core glass its basic properties.
The optional constituents defined in the claims are used to fine-tune the basic properties and/or to give the glass extra properties without its properties being affected.
For the envisaged object, a glass having the composition as defined in claim 8 has been found to be very suitable, which a refractive index n of 1.8, an American softening point at 718xc2x0 C. and an intrinsic transmission Ti of at least 0.99. Core glass rods may be drawn from molten liquid having the desired composition. An alternative is to mold the molten liquid in special molds. Light transmission glass fibers can be manufactured by means of the core glass according to the invention and a cladding glass in accordance with known methods, for example, a double crucible method or a rod-in-tube method. A bundle of fibers can be made from a plurality of glass fibers. By twisting a bundle of fibers, a twister is obtained. This twister rotates the image coming from, for example, a photomultiplier and is used in night-vision telescopes. To be able to comply with all of these manufacturing steps, a special core glass is necessary which must also be free from Cd in the present case. A bundle of fibers, which is twisted or not twisted, can also be given a cross-section extending from small to large. Then a bundle of fibers referred to as taper is concerned.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.